The present invention relates to a method for operating a hybrid drivetrain for a motor vehicle, in which power is provided by an internal combustion engine in a first operating mode and power is provided by an electric machine in a second operating mode, wherein a change from one operating mode into the other operating mode is carried out according to the state of the drivetrain and/or the motor vehicle.
In the field of drivetrains for motor vehicles, what are known as hybrid drivetrains have long been known. These have a first drive unit, in the form an internal combustion engine for generating driving power, and also a second drive unit, which contains an electric machine arrangement.
Besides what are known as mild hybrid concepts, in which an electric machine is only used to assist the internal combustion engine, full hybrid concepts are also known. In full hybrid concepts the vehicle can be driven either only by means of the internal combustion engine or only by means of the electric machine arrangement and, where necessary, in mixed hybrid operation. This type of hybrid drivetrain will be used as a general basis in the present case.
The operation of an internal combustion engine in a motor vehicle typically requires a start-up clutch and a gear box. Here, it is known to form the gear box steplessly. It is also known to combine the internal combustion engine with an automated shifting gear box, for example an automatic shift gearbox (ASG), a twin-clutch gearbox (TCG), or a torque-converter automatic gearbox.
In the case of hybrid drivetrains, it is generally sought to drive the vehicle predominantly in the second operating mode, in which driving power is provided by the electric machine. The “bottle neck” in this case is usually the electric power source, which is generally formed as a battery.
Furthermore, it is generally possible to operate the internal combustion engine and the electric machine in parallel in a third operating mode. In what is known as a boost mode, driving power is provided in this case both by the internal combustion engine and also the electric machine. There is also the possibility in such a third operating mode to shift the load point of the internal combustion engine, wherein excess power is provided that can be used for example to charge the battery.
In the case of hybrid drivetrains of this type, it is generally also sought to carry out a regeneration (recuperating) operation during a braking process, such that the moment of inertia of the travelling vehicle is converted into regenerative power that can in turn be used to charge the battery.
Here, the change between operating modes is generally carried out by various control devices.
For example, it is known from document DE 100 35 027 A1 to carry out the selection of the operating mode on the basis of vehicle dynamics, driver behavior and available electric driving power, and additionally the route profile covered by the vehicle as a criterion for the selection of the operating mode. It is also known from this document to perform the transition to electromotive drive by decoupling the internal combustion engine after a period of delay, which is dependent on the route profile. It is also known from this document to perform the transition to internal-combustion-engine-powered operation or mixed operation after a period of delay dependent on the route profile.
It is also known from document DE 101 53 509 A1 for the controller controlling the charging of the battery to define a number of threshold values and to compare the status-of-charge with these threshold values in order to determine the operating mode of a starter/generator connected to the engine.
Document DE 601 29071 T2 discloses a vehicle control system for performing the transition between operating modes according to detected abnormalities in the drivetrain.
Document DE 10 2008 202842 A1 further discloses the provision, in a mild hybrid drivetrain, of a control device for switching between at least two operating modes, said control device being coupled to the brake pedal and designed in such a way that, in a first operating mode, the setting for the driving torque can be varied according to the position of the brake pedal.
It is also known (DE 10 2009 004 671 A1) to operate a drive system of a motor vehicle in a charge sustaining mode and a charge depletion mode, wherein the charge sustaining mode is requested when a piece of information concerning an anticipated environment meets a specific criterion.
Lastly, document DE 10 2006 034 933 A1 discloses a method for controlling a hybrid drivetrain, in which a plurality of control parameter sets having different target statuses of charge for a high-capacity battery is provided, wherein a respective operating mode of the vehicle is associated with the plurality of control parameter sets and a present operating mode is defined, wherein a control parameter set corresponding to the present operating mode is used to control a charging mode of the high-capacity battery with a corresponding target status-of-charge.